Shortest description is that positioned sketch allow you to rotate and move sketch as you wish. Pictures added and details coming soon.
Create sketch on the XY plane.
Give it 20 mm thinkness with Pad command. And Create new sketch on the surface of Pad (shown with yellow arrow in picture)
Your new sketch will came screen like this. And exit workbench.
If i want to rotate part and attach new sketch by rotating axis 90 degree, i must use positioned sketch command. Run positioned sketch and select same surface on Pad.
İf you click "Reverse V" and "Swap" on the positioned sketch menu, the axis of the sketch will rotate 90 degree (Check the yellow circle).
And your new positioned sketch will came screen like this (part rotated). And exit workbench.
If you want to move or change the axis of the sketch which has already created, you must right click to the sketch. And you must select Change sketch support from "Sketch.X Object"
Sketch positioning menu will pop up. You can move sketch another plane or surface with "Sliding" in type options. And you can change sketch axis with "Positioned" in type options.